Flame-retarded olefin polymers and additive systems therefor

ABSTRACT

FLAME-RETARDED OLEFIN POLYMERS ARE PROVIDED BY ADMIXING WITH THE POLYMER A FLAME-RETARDANT ADDITIVE SYSTEM WHICH CONSISTS ESSENTIALLY OF (A) A COMPOUND OF THE FORMULA   BRCH2-C(-CH2BR)2-CH2-O-(CH2-C(-CH2BR)2-CH2-O)N-CH2-   C(-CH2BR)3   WHEREIN N IS 0 TO 5 AND (B) ANTIMONY TRIOXIDE.

United States Patent 3,700,625 FLAME-RETARDED OLEFIN POLYMERS AND ADDITIV E SYSTEMS THEREFOR DOllllle G. Brady, Ernest A. Zuech, and Roy A. Gray, Bartlesville, 0kla., assignors to Phillips Petroleum Company No Drawing. Filed Aug. 30, 1971, Ser. No. 176,259 Int. Cl. C08f 45/58 US. Cl. 26045.75 R Claims ABSTRACT OF THE DISCLOSURE Flame-retarded olefin polymers are provided by admixing with the polymer a flame-retardant additive system which consists essentially of (A) a compound of the formula wherein n is 0 to 5 and (B) antimony trioxide.

It is known that bromine-containing compounds are generally effective flame-retardant additives for polyolefins, particularly for polypropylene. However, most compounds of this type have limitations due to their thermal instability which restricts the maximum processing temperature which can be employed. In addition, it has been found that many such bromine compounds, while providing a flame-retardancy effect, are unsuitable because of their tendency to cause degradation of the polymer. This adverse effect can be readily observed by the increase in the melt flow number of the polymer composition. Thus, an additive system capable of providing a fiame-retardancy elfect to the polymer while at the same time avoiding an adverse effect on the melt flow number of the polymer composition, and which would be processable at elevated temperatures, would be a significant contribution to the art.

Accordingly, it is an object of this invention to provide a novel flame-retardant additive system for polyolefins.

It is a further object of this invention to provide a novel ame-retarded composition of polyolefins.

Other aspects, objects and advantages of the invention will be readily apparent to those skilled in the art from a reading of the following disclosure.

In accordance with the present invention, w have discovered that flame-retarded compositions of olefin polymers having a minimal alteration of their melt flow number are obtained by admixing with the olefin polymer an additive system Which consists essentially of (A) a compound of the formula CH Br l l More particularly, we have now discovered that utilization of the additive system consisting of the combination of the brominated compounds (A) as above described and (B) antimony trioxide as a flame retardant for olefin polymers, particularly for polypropylene, results in a polymeric composition which is not only flame-retarded but is not subject to polymer deterioration under conditions of fabrication. The degree of polymer deterioration or degradation can be readily determined by measuring the increase effected on the melt flow number (MFN) (AST M D 1238-65T, Test Condition L) of the final polymer composition containing the additive system when elevated to the temperature range generally employed in 3,700,625 Patented Oct. 24, 1972 fabrication processes. In addition, the additive system of this invention has the further advantage that its use in the polymer composition does not cause an adverse effect on the color thereof.

In one presently preferred embodiment of the present invention, the additive system to be employed with the polymer is hexabromodipentaerythritol when n is 0 in formula (A) above and the polymer is preferably a normally solid polymer of propylene.

The brominated compounds (A) as employed in the additive system are known chemical compounds which can be readily prepared from the corresponding hydroxy compounds by reaction with phosphorus tribromide. Other brominating agents that can be used as alternates to PBr are thionyl bromide, mixtures of bromine with red phosphorus, hydrogen bromide in glacial acetic acid, and aqueous hydrobromic acid employed in such amounts and at sufiiciently low temperatures to avoid cleavage of the ether bonds.

Examples of compounds of formula (A) in addition to hexabromodipentaerythritol (HBDP) are:

n: Compounds 1 Octabromotripentaerythritol. 2 Decabromotetrapentaerythritol. 3 Dodecabromopentapentaerythritol. 4 Tetradecabromohexapentaerythritol. 5 Hexadecabromoheptapentaerythritol.

The additive system of this invention is prepared by mixing at least one compound of formula (A) and antimony trioxide in amounts such that the weight ratio of A:B is in the range of 1:1 to 5:1.

In utilizing the additive system herein, there is no definite upper limit for the amount of total additives to be employed, so long as the properties of the polymeric composition required for a particular use are retained. Ordinarily, the additives are used at the lowest level which will provide the desired degree of retardancy. The following ranges are generally employed:

Broad 1 Preferred X Bromo(polypentaerythritol) 1 15 The upper limit of total additive incorporated into any normally solid olefin polymer will vary with each host material. However, for one presently preferred embodiment of this invention, the preferred ranges listed above are those which have been found to be most applicable to polypropylene.

The production of the flame-retarded compositions can be carried out in various manners, readily apparent to those skilled in the art. For example, intimate mixture of the polymer and flame-retarding additive according to this invention can be achieved by mixing the various additives with the polymer at an elevated temperature in an extrusion press or kneader. Since the incorporation of flame retardants in general with polymers is a technique well known in the art, the mode of mixing the ingredients constituting the novel compositions of this invention is not considered a part of this disclosure.

The flame-retarded compositions of this invention are useful for a variety of purposes such as in the production of electrical insulating compositions for house wiring, small appliances, electronic equipment wire insulation, iacketing and the like. In addition, the compositions formed of polypropylene are further particularly useful in fiber production wherein a significant alteration of the melt flow values of the polymer and/or the color thereof are sought to be avoided.

It is to be understood that the compositions of this invention can contain, in addition to the flame-retardant system, other additives such as certain fillers, dyes, pigments, plasticizers, antioxidants, antistatic agents and The above data show that HBDP imparts reduced flammability to olefin polymers. In addition, when taken in combination with the data of Example I, the system is shown to be particularly elfective in its achievement of the like. Such compounds are well known in the art thermal stability in addition to flammability reduction of and, for the sake of brevity, will not be repeated here. olefin polymers.

The polyolefins which can be made flame-retardant ac- Reasonable variation and modification are possible cording to this invention are polymers of mono-alphawithin the foregoing disclosure without departing from the olefins having the general formula CH CHR wherein R spirit or scope thereof. represents hydrogen or an aryl radical or an alkyl radical We claim: or combinations thereof such as alkaryl and aralkyl hav- 1. A flame-retardant additive system which consists ing up to a total of 10 carbon atoms in each R group. essentially of (A) a compound of the formula Typical polymers are the homopolymers and copolymers cHzBr CHZBI CHzBr of ethylene, propylene, butene-l, isobutylene, pentene-l, I J I 4-methylpentene-l, styrene, and dimethylstyrene. BrCHP I CH2 O CH2T TCHFOTCHT'CTCHBI The following examples will further illustrate the in- CHzB! L CHzBr H2131- vention, although they are not to be construed as limiting wherein n is 0 to 5 and (B) antimony trioxide the Scope thereof- 2. An additive system according to claim 1 wherein EXAMPLE I said compounds (A) is hexabromodipentaerythritol.

A series of 30 g. lots of commercially available white Aflame'retarded Composition Comprising anol'mally polypropylene containing 0.3 weight percent tetrakis P y of one more 9- P =9 P- methylene(3,5 di-tert-butyl-4-hydroxy hydrocinnamate). taming from 2 to 12 carbon atoms havmg admlxed therein methane and f 0 0 to 0 weight percent f antia flame-retardant additive system conslsting essentially of oxidants and stabilizers and having a melt flow value of from 1 to 15 P P- Of a COmPOImd of the formula about 4.0 g./l0 min. (ASTM D 1238-62T, Condition L) Erma. ZH Br 0mm were dry blended on a two-roll mill at 320360 F. with the flame-retardant additive system as shown in Table I BrCHZ CH2 0 L II il CH? CHZBI below. The resulting blends were then compression H231 H213 molded at 325-375" F. into sheets As-inch thick from wherein n is 0 to 5 and (B) from 1 to 15 php. of antimony which samples were cut. The burning characteristics of trioxide. the samples were determined by the method of ASTM 4. A flame-retarded composition according to claim 3 D 635-63 and the Limiting Oxygen Index method (C. P. wherein said olefin polymer is polypropylene and said Fenimore and F. J. Martin, Modern Plastics 43, 141, compound (A) is hexabromodipentaerythritol. November 1966). The Limiting Oxygen Index (L.O.I.) 5. A flame-retarded composition according to claim 4 is the minimum volume fraction of oxygen required in 39 wherein compound (A) is present in an amount of from an oxygen/nitrogen atmosphere to sustain burning of a 2 to 5 php. and compound (B) is present in an amount plastic test sample. The following results were obtained. of from 1 to 2.5 php.

TABLE I Thermal stability Color MFN Retardant Run No. (emulation 450 )3. 470 F. 490 F 450 F. 410 F. 490 F.

1 2php.IHBDP, White White White 5.1 5.8 7.5

1 php. SbzOa. 2 None (control).- Colorless Colorless Colorless 3. 6-4.4 3. 6-4.4 3. 6-4.4

(translucent). (translucent). (translucent).

n Hexabromodlpentaerythritol.

The above data clearly demonstrate that the additive References Cited system of this invention produces a thermally stable UNITED STATES PATENTS polymer having good color properties at ordmary Processing temperatures 3,337,495 8/1967 Corbett et a1 260--45.95

2,600,455 6/1952 Wilson et al 26033.2 EXAMPLE II 2,962,464 11/1960 Felid 260 .45.95

A further series of olefin compositions were prepared, 3,642,868 2/ 1972 l' t 260-4585 using commercially available polypropylene, in accordance with the process described in Example I. The fiame- DONALD CZAJA Pnmary Exammer retardant system consisted of a combination of hexa- V, P, HOKE, A i t E i bromo-dipentaerythritol and antimony trioxide. The resulting samples were tested to determine the efiect of the US. Cl. X.R. additive system on the flammability of the composition, using the Limiting Oxygen Index procedure described in 252 260 41 R Example I. The following results were obtained.

TABLE 11 Run No 3 1 15. 2 11? L.o.r.- 2333313313111113333: 5 5 I??? CERTIFICATE OF CORRECTION Patent No. 3,700,625 Dated: October 21;, 1972 It is certiiied that error appears in the above-identified patent and that said letters Patent are hereby corrected as show below:

Claims 1 and 3, the subscript ---n-- should be inserted immediately following the bracket in the structural formula...

Signed and sealed this 19th day of February 197L (SEAL) Attest EDWARD M.FLETOHER,JR. I C MARSHALL DANN Atte sting Officer Commissioner of Patents CERTIFICATE OF CORRECTION Patent No. 3,700,625 Dated: October 21;, 1972 It is certiiied that error appears in the above-identified patent and that said letters Patent are hereby corrected as show below:

Claims 1 and 3, the subscript ---n-- should be inserted immediately following the bracket in the structural formula...

Signed and sealed this 19th day of February 197L (SEAL) Attest EDWARD M.FLETOHER,JR. I C MARSHALL DANN Atte sting Officer Commissioner of Patents UNITED STATES PAiENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,700,625 Ila-Wm October 21;, 1972 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as sham below:

n--- should be inserted Claims 1 and 3, the subscript immediately following the bracket in the structural formula.

(SEAL) Attest:

EDWARD M.FLETCIER,JR. C. MARSHALL DANN I Attesting Officer Commissioner of Patents 

